The present invention relates to a semiconductor integrated circuit device and to a manufacture technology for the same and, specifically, to a technology which is effectively applied to a semiconductor integrated circuit device comprising a silicon oxynitride film as a gate insulating film for MISFET (Metal Insulator Semiconductor Field Effect Transistor).
To realize the low-voltage operation of MISFET, a gate oxide film must be made thinner in proportion to a reduction in the thickness of MISFET. However, when the thickness of the gate oxide film is reduced, a direct tunnel current running through the film grows, thereby causing a gate leak current which cannot be ignored from the viewpoint of reducing power consumption.
To cope with this, attempts have been made to increase the physical thickness of the gate insulating film by using a high dielectric film such as a titanium oxide (TiO2) or tantalum oxide (Ta2O5) film having a higher relative dielectric constant than silicon oxide. However, as the gate insulating film formed of this high dielectric film has many problems with interfacial control and the like, use of this film in mass-produced devices is currently considered to be difficult.
Since a silicon oxynitride film formed by nitriding part of a silicon oxide film has a higher dielectric constant than silicon oxide, the effect of reducing a leak current by increasing the physical thickness of a gate insulating film can be expected from this film. It is reported that a gate insulating film formed of a silicon oxynitride film is effective in the suppression of boron leakage that an impurity (boron) contained in a p type gate electrode goes through the channel area of a substrate by a heat treatment during the process, the improvement of hot carrier resistance of MISFET and the improvement of the electron mobility of an n channel type MISFET.
As means of nitriding a gate insulating film made from silicon oxide, there is known a method in which a substrate is heated in a high-temperature atmosphere of around 1,000° C. containing an NO (nitrogen monoxide) gas after a silicon oxide film is formed on the silicon substrate.
Japanese Unexamined Patent Publication No. 2001-332724 discloses a technology for forming a gate insulating film from silicon oxynitride having two peaks of nitrogen concentration at the interface with a silicon substrate and in the film, to prevent the penetration of boron contained in the p type gate electrode and to improve hot carrier resistance, in an MIS device having a so-called dual gate structure using an n type gate electrode as an n channel MISFET and a p type gate electrode as a p channel MISFET.
To form the above silicon oxynitride film, the silicon substrate is first wet oxidized to form a silicon oxide film having a thickness of about 7 nm on the surface, heated in an atmosphere containing an NO gas to segregate nitrogen at the interface between the silicon oxide film and the substrate, and dry oxidized. When this dry oxidation is carried out, the interface between the silicon oxide film and the substrate is oxidized to form a silicon oxide film having a thickness of 1 to 2 nm underlying an area where nitrogen has been segregated. Thereafter, when the substrate is heated in an atmosphere containing an NO gas again, nitrogen is segregated at the interface between the silicon oxide film underlying the area where nitrogen has been segregated and the substrate, thereby obtaining a gate insulating film made of silicon oxynitride and having two peaks of nitrogen concentration at the interface with the silicon substrate and in the film.
Japanese Unexamined Patent Publication No. 2000-357688 discloses a technology for forming a gate insulating film from silicon oxynitride having two peaks in nitrogen concentration distribution in the thickness direction by a method different from that of the above publication.
In this publication, the silicon substrate is first heated in an oxygen atmosphere to form a silicon oxide film having a thickness of about 5 nm on the surface and heated in an NO gas atmosphere to form a silicon oxynitride film having a thickness of about 5.5 nm having a peak of nitrogen concentration near the interface with the substrate. Thereafter, the surface of this silicon oxynitride film is etched with a hydrofluoric acid aqueous solution to remove its surface layer portion, thereby obtaining a silicon oxynitride film having a thickness of about 1 nm and containing nitrogen in the entire thickness direction in large quantities. Thereafter, a second heat treatment is carried out in an NO gas or N2O gas atmosphere to grow a new thermally oxidized film on the substrate and introduce nitrogen into the thermally oxidized film, thereby obtaining a silicon oxynitride film having two peaks in nitrogen concentration distribution in the thickness direction.
Japanese Unexamined Patent Publication No. Hei 8(1996)-167664 (U.S. Pat. No. 5,591,681) discloses a technology for forming a silicon oxide film containing nitrogen by heating in a NO or N2O gas atmosphere.